1. Field of the Invention
The present invention relates to solid-state electronics, and, in particular, to MOSFET-based logic devices.
2. Description of the Related Art
Recently, several new devices have been proposed to increase the functional density of integrated circuits. For example, U.S. Pat. No. 4,999,687 (Luryi et al.) ("the '687 patent") describes a three-input solid-state logic device that performs the logical operation of Expression (1) as follows: EQU (X+Y+Z)'+(XYZ) (1)
where X, Y, and Z are the three logical inputs to the device. The first half of Expression (1) (i.e., (X+Y+Z)') is a NOR operation, while the second half (i.e., (XYZ)) is an AND operation. As such, the device of Expression (1), which performs the logical sum of NOR and AND, and may be called a NORAND device. The functionality of logic devices, such as the NORAND device, may reduce both the number of elements and the complexity of logic circuits built with such logic devices.
The NORAND device of the '687 patent relies on the characteristics of a charge injection transistor (CHINT), such that real space transfer occurs when carriers spill over an energy barrier that is part of the heterostructure of the CHINT. There are several disadvantages of CHINT implementations. First, pure CHINT logic has drawbacks like power dissipation and needing level shifting of outputs after a few stages of logic, since the logic "zero" cannot be preserved through multiple stages. Additionally, there would be a need for memory and other things that may not be easily implemented in a single CHINT technology.